[llvm] [NVPTX] Fix code generation for `trap-unreachable`. (PR #67478)
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Wed Sep 27 00:41:14 PDT 2023
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-selectiondag
<details>
<summary>Changes</summary>
https://reviews.llvm.org/D152789 added an `exit` op before each `unreachable`. This means we never get to the `trap` instruction.
- When `trap-unreachable` is enabled and `no-trap-after-noreturn` is not, don't insert `exit` before each `unreachable`.
- Lower ISD::TRAP to both `trap` and `exit` instead of just the former.
The fix doesn't work with `no-trap-after-noreturn`, because the `unreachable`s not following a `noreturn` are lowered to `exit; trap; exit;`.
An alternative approach would be to insert `trap`s in `NVPTXLowerUnreachablePass`, depending on the `trap-unreachable` and `no-trap-after-noreturn` settings. I think we would then want skip lowering ISD::TRAP, so that we don't end up with `trap; exit; trap;` sequences.
---
Full diff: https://github.com/llvm/llvm-project/pull/67478.diff
5 Files Affected:
- (modified) llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp (+1-6)
- (modified) llvm/lib/Target/NVPTX/NVPTX.h (+2-1)
- (modified) llvm/lib/Target/NVPTX/NVPTXLowerUnreachable.cpp (+38-7)
- (modified) llvm/lib/Target/NVPTX/NVPTXTargetMachine.cpp (+3-9)
- (modified) llvm/test/CodeGen/NVPTX/unreachable.ll (+12-3)
``````````diff
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index f39b62abdd87790..ba0ab3586f75825 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -3226,14 +3226,9 @@ void SelectionDAGBuilder::visitUnreachable(const UnreachableInst &I) {
// We may be able to ignore unreachable behind a noreturn call.
if (DAG.getTarget().Options.NoTrapAfterNoreturn) {
- const BasicBlock &BB = *I.getParent();
- if (&I != &BB.front()) {
- BasicBlock::const_iterator PredI =
- std::prev(BasicBlock::const_iterator(&I));
- if (const CallInst *Call = dyn_cast<CallInst>(&*PredI)) {
+ if (const CallInst *Call = dyn_cast_or_null<CallInst>(I.getPrevNode())) {
if (Call->doesNotReturn())
return;
- }
}
}
diff --git a/llvm/lib/Target/NVPTX/NVPTX.h b/llvm/lib/Target/NVPTX/NVPTX.h
index c5816b9266dfd9e..8dc68911fff0c05 100644
--- a/llvm/lib/Target/NVPTX/NVPTX.h
+++ b/llvm/lib/Target/NVPTX/NVPTX.h
@@ -47,7 +47,8 @@ MachineFunctionPass *createNVPTXReplaceImageHandlesPass();
FunctionPass *createNVPTXImageOptimizerPass();
FunctionPass *createNVPTXLowerArgsPass();
FunctionPass *createNVPTXLowerAllocaPass();
-FunctionPass *createNVPTXLowerUnreachablePass();
+FunctionPass *createNVPTXLowerUnreachablePass(bool TrapUnreachable,
+ bool NoTrapAfterNoreturn);
MachineFunctionPass *createNVPTXPeephole();
MachineFunctionPass *createNVPTXProxyRegErasurePass();
diff --git a/llvm/lib/Target/NVPTX/NVPTXLowerUnreachable.cpp b/llvm/lib/Target/NVPTX/NVPTXLowerUnreachable.cpp
index 1d312f82e6c061c..efafd909b93be37 100644
--- a/llvm/lib/Target/NVPTX/NVPTXLowerUnreachable.cpp
+++ b/llvm/lib/Target/NVPTX/NVPTXLowerUnreachable.cpp
@@ -72,6 +72,7 @@
#include "llvm/IR/Function.h"
#include "llvm/IR/InlineAsm.h"
#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/Type.h"
#include "llvm/Pass.h"
@@ -83,14 +84,19 @@ void initializeNVPTXLowerUnreachablePass(PassRegistry &);
namespace {
class NVPTXLowerUnreachable : public FunctionPass {
+ StringRef getPassName() const override;
bool runOnFunction(Function &F) override;
+ bool shouldEmitTrap(const UnreachableInst &I) const;
public:
static char ID; // Pass identification, replacement for typeid
- NVPTXLowerUnreachable() : FunctionPass(ID) {}
- StringRef getPassName() const override {
- return "add an exit instruction before every unreachable";
- }
+ NVPTXLowerUnreachable(bool TrapUnreachable, bool NoTrapAfterNoreturn)
+ : FunctionPass(ID), TrapUnreachable(TrapUnreachable),
+ NoTrapAfterNoreturn(NoTrapAfterNoreturn) {}
+
+private:
+ bool TrapUnreachable;
+ bool NoTrapAfterNoreturn;
};
} // namespace
@@ -99,6 +105,24 @@ char NVPTXLowerUnreachable::ID = 1;
INITIALIZE_PASS(NVPTXLowerUnreachable, "nvptx-lower-unreachable",
"Lower Unreachable", false, false)
+StringRef NVPTXLowerUnreachable::getPassName() const {
+ return "add an exit instruction before every unreachable";
+}
+
+// =============================================================================
+// Returns whether a `trap` intrinsic should be emitted before I.
+//
+// This is a copy of the logic in SelectionDAGBuilder::visitUnreachable().
+// =============================================================================
+bool NVPTXLowerUnreachable::shouldEmitTrap(const UnreachableInst &I) const {
+ if (!TrapUnreachable)
+ return false;
+ if (!NoTrapAfterNoreturn)
+ return true;
+ const CallInst *Call = dyn_cast_or_null<CallInst>(I.getPrevNode());
+ return Call && Call->doesNotReturn();
+}
+
// =============================================================================
// Main function for this pass.
// =============================================================================
@@ -109,18 +133,25 @@ bool NVPTXLowerUnreachable::runOnFunction(Function &F) {
LLVMContext &C = F.getContext();
FunctionType *ExitFTy = FunctionType::get(Type::getVoidTy(C), false);
InlineAsm *Exit = InlineAsm::get(ExitFTy, "exit;", "", true);
+ Function *Trap = nullptr;
bool Changed = false;
for (auto &BB : F)
for (auto &I : BB) {
if (auto unreachableInst = dyn_cast<UnreachableInst>(&I)) {
- Changed = true;
+ if (shouldEmitTrap(*unreachableInst)) {
+ if (!Trap)
+ Trap = Intrinsic::getDeclaration(F.getParent(), Intrinsic::trap);
+ CallInst::Create(Trap, "", unreachableInst);
+ }
CallInst::Create(ExitFTy, Exit, "", unreachableInst);
+ Changed = true;
}
}
return Changed;
}
-FunctionPass *llvm::createNVPTXLowerUnreachablePass() {
- return new NVPTXLowerUnreachable();
+FunctionPass *llvm::createNVPTXLowerUnreachablePass(bool TrapUnreachable,
+ bool NoTrapAfterNoreturn) {
+ return new NVPTXLowerUnreachable(TrapUnreachable, NoTrapAfterNoreturn);
}
diff --git a/llvm/lib/Target/NVPTX/NVPTXTargetMachine.cpp b/llvm/lib/Target/NVPTX/NVPTXTargetMachine.cpp
index cad97b1f14eb2b9..8d895762fbe1d9d 100644
--- a/llvm/lib/Target/NVPTX/NVPTXTargetMachine.cpp
+++ b/llvm/lib/Target/NVPTX/NVPTXTargetMachine.cpp
@@ -63,13 +63,6 @@ static cl::opt<bool> UseShortPointersOpt(
"Use 32-bit pointers for accessing const/local/shared address spaces."),
cl::init(false), cl::Hidden);
-// FIXME: intended as a temporary debugging aid. Should be removed before it
-// makes it into the LLVM-17 release.
-static cl::opt<bool>
- ExitOnUnreachable("nvptx-exit-on-unreachable",
- cl::desc("Lower 'unreachable' as 'exit' instruction."),
- cl::init(true), cl::Hidden);
-
namespace llvm {
void initializeGenericToNVVMLegacyPassPass(PassRegistry &);
@@ -410,8 +403,9 @@ void NVPTXPassConfig::addIRPasses() {
addPass(createSROAPass());
}
- if (ExitOnUnreachable)
- addPass(createNVPTXLowerUnreachablePass());
+ const auto &Options = getNVPTXTargetMachine().Options;
+ addPass(createNVPTXLowerUnreachablePass(Options.TrapUnreachable,
+ Options.NoTrapAfterNoreturn));
}
bool NVPTXPassConfig::addInstSelector() {
diff --git a/llvm/test/CodeGen/NVPTX/unreachable.ll b/llvm/test/CodeGen/NVPTX/unreachable.ll
index 742089df1bd4533..011497c4e23401a 100644
--- a/llvm/test/CodeGen/NVPTX/unreachable.ll
+++ b/llvm/test/CodeGen/NVPTX/unreachable.ll
@@ -1,5 +1,11 @@
-; RUN: llc < %s -march=nvptx -mcpu=sm_20 -verify-machineinstrs | FileCheck %s
-; RUN: llc < %s -march=nvptx64 -mcpu=sm_20 -verify-machineinstrs | FileCheck %s
+; RUN: llc < %s -march=nvptx -mcpu=sm_20 -verify-machineinstrs \
+; RUN: | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-NOTRAP
+; RUN: llc < %s -march=nvptx64 -mcpu=sm_20 -verify-machineinstrs \
+; RUN: | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-NOTRAP
+; RUN: llc < %s -march=nvptx -mcpu=sm_20 -verify-machineinstrs -trap-unreachable \
+; RUN: | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-TRAP
+; RUN: llc < %s -march=nvptx64 -mcpu=sm_20 -verify-machineinstrs -trap-unreachable \
+; RUN: | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-TRAP
; RUN: %if ptxas && !ptxas-12.0 %{ llc < %s -march=nvptx -mcpu=sm_20 -verify-machineinstrs | %ptxas-verify %}
; RUN: %if ptxas %{ llc < %s -march=nvptx64 -mcpu=sm_20 -verify-machineinstrs | %ptxas-verify %}
@@ -11,7 +17,10 @@ define void @kernel_func() {
; CHECK: call.uni
; CHECK: throw,
call void @throw()
-; CHECK: exit
+; CHECK-TRAP-NOT: exit;
+; CHECK-TRAP: trap;
+; CHECK-NOTRAP-NOT: trap;
+; CHECK: exit;
unreachable
}
``````````
</details>
https://github.com/llvm/llvm-project/pull/67478
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